The present invention relates to a fingerprint correlator, and in particular to an optical fingerprint correlator and the method for correlating fingerprints by optical means.
The prior art of fingerprint identification and correlation encompasses a wide variety of techniques for examining and comparing a large database of fingerprint information containing known fingerprint characteristics with an unknown fingerprint. Because of the large amounts of data required to characterize each individual print a substantial computer commitment is required for handling, storage, and processing of such data. Typically, fingerprint identification processing of such large amounts of data requires the use of a mainframe computer. Thus a substantial computer commitment in terms of hardware, software, operating and support expense, and processing time relating to the fact that this massive amount of data typically must be handled by serial operating computers is required. The quality of correlation possible from the use of prior art fingerprint correlation techniques is a function of the amount of data used to characterize each individual print. Thus, the more data per print, theoretically, the better the overall characterization of each print. In fact, for legal purposes, a specific number of fingerprint characteristics must be established in order for the correlation to be deemed valid. Because of the importance of fingerprint identification, large commitments of time, money, and resources are typically found to be acceptable when considered in relation to the alternative manual examination techniques of the past.
A generalized explanation of the prior art fingerprint identification process will help to provide the reader with some insight as to the complexities of the prior art process. First, an unknown fingerprint is loaded by means of a digitizing scanner, or similar device, into a computer. Second, the fingerprint information obtained from the digitizer is divided into pixels. Thus, the fingerprint image would be divided into a number of pixels, the number of which would relate to the quality of the result desired. Third, each of the pixels would be assigned a vector having magnitude and directional information in relation to the surrounding characteristics of the fingerprint. Thus, typically for each fingerprint there would be a substantial number of vectors characterizing its image. Fourth, all of the vectors of the unknown print would then be compared by the computer to the vectors of the known fingerprint. In the past, this comparison using existing computers would be performed serially, and thus can be seen to be a time-consuming process when a large number of prints would be required to be compared with the single unknown fingerprint. Fifth, the comparison results determined by the computer could then be displayed to show the quality of the match between the unknown and the known fingerprint. In the prior art, techniques have been used to shorten the process and to make it more efficient by using methods which would permit pre-sorting fingerprints by certain types of characteristics, and then zeroing in within the limited group for comparison with the unknown fingerprint. All such techniques, however, are found to be very time-consuming and expensive in terms of resource commitments.
In U.S. Pat. No. 4,790,564, an automatic method and related apparatus for identifying fingerprints is disclosed. The method and apparatus identified the fingerprints by means of comparing the minutiae of each fingerprint in a database of fingerprints with selected ones of pre-computed vector images of search minutiae in a search print to be identified. The system determines the probability of a match by comparing the position and angle of the minutiae being compared between the database file print and the unknown print.
In U.S. Pat. No. 4,690,554, the invention is a device employing the optical auto-correlation method for automatically comparing the fingerprint of an individual with a previously identified exemplar utilizing a pair of multifaceted mirrors rotating about mutually perpendicular axes to sweep an image of the fingerprint over the surface of the exemplar in a raster. A novel optical means is used to compensate for possible angular misalignment of the fingerprint and the exemplar.
U.S. Pat. No. 4,641,350 describes a fingerprint identification system which uses a scanner, a memory for storing data representative of fingerprints received from the scanner, means for comparing newly received data to reference data, and means for determining the degree of distortion and misregistration present in the new data relative to the reference data. The technique disclosed allows the reference array to be stretched and/or compressed to account for distortion or misregistration in the new data array. The new data and the reference data are stored in arrays which are compared by a method which includes dividing the reference array into subarrays and comparing the elements of each subarray with the elements of a number of subarrays of the new data array.
It can thus be seen from this brief review of the prior art that in addition to a large database and a substantial computer commitment for serial comparisons of "minutiae or substantial arrays of digitized data", a methodology and apparatus for accomplishing the correlation results desired by a less tedious and data-intensive technique would be most productive. Thus, a gross data handling methodology analogous to a parallel computer process might be considered a more desirable approach. The present invention, however, provides a methodology of handling the characterization information about each known and unknown print in such a way that parallel computing processes are either totally unnecessary or may be used to advantage to speed up the comparison process even more than without it. Thus, where under the best of conditions using prior art technology, perhaps as many as one hundred to a thousand fingerprints per minute may be compared, the present invention permits a thousand or more fingerprints to be compared per second.